void main() {
  var str = 'this is string'; //'',"",''' ''',""" """都可以，最后二种支持换行
  String str1 = 'this also is string';
  String str2 = '''this also is string
      this also is string
    ''';
  // print(str2);
  //1.字符串拼接
  //print('$str $str2');
  //2.字符串拼接
  print(str + " " + str1);
}
